Surface formed complex polymer lenses for visible light diffusion

ABSTRACT

Disclosed is a transparent polymeric film having a top and bottom surface comprising a plurality of complex lenses on at least one surface thereof. Such a film is useful for diffusing light such as necessary in an LC display device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is one of a group of seven applications co-filed underSer. Nos. 10/095,204, 10/095,601, 10/095,145, 10/095,172, 10/095,319,10/094,977 and 10/094,979.

FIELD OF THE INVENTION

The invention relates to a transparent polymeric film having a top andbottom surface, at least one surface comprising a plurality of complexlenses thereon suitable to diffuse specular light.

BACKGROUND OF THE INVENTION

Optical structures that scatter or diffuse light generally function inone of two ways: (a) as a surface diffuser utilizing surface roughnessto refract or scatter light in a number of directions; or (b) as a bulkdiffuser having flat surfaces and embedded light-scattering elements.

A diffuser of the former kind is normally utilized with its roughsurface exposed to air, affording the largest possible difference inindex of refraction between the material of the diffuser and thesurrounding medium and, consequently, the largest angular spread forincident light. However, some prior art light diffusers of this typesuffer from a major drawback: the need for air contact. The requirementthat the rough surface must be in contact with air to operate properlymay result in lower efficiency. If the input and output surfaces of thediffuser are both embedded inside another material, such as an adhesivefor example, the light-dispersing ability of the diffuser may be reducedto an undesirable level.

In one version of the second type of diffuser, the bulk diffuser, smallparticles or spheres of a second refractive index are embedded withinthe primary material of the diffuser. In another version of the bulkdiffuser, the refractive index of the material of the diffuser variesacross the diffuser body, thus causing light passing through thematerial to be refracted or scattered at different points. Bulkdiffusers also present some practical problems. If a high angular outputdistribution is sought, the diffuser will be generally thicker than asurface diffuser having the same optical scattering power. If howeverthe bulk diffuser is made thin, a desirable property for mostapplications, the scattering ability of the diffuser may be too low.

Despite the foregoing difficulties, there are applications where asurface diffuser may be desirable, where the bulk type of diffuser wouldnot be appropriate. For example, the surface diffuser can be applied toan existing film or substrate thus eliminating the need to for aseparate film. In the case of light management in a LCD, this increasesefficiency by removing an interface (which causes reflection and lostlight).

U.S. Pat. No. 6,270,697 (Meyers et al.), blur films are used totransmitted infrared energy of a specific waveband using a repeatingpattern of peak-and-valley features. While this does diffuse visiblelight, the periodic nature of the features is unacceptable for abacklight LC device because the pattern can be seen through the displaydevice.

U.S. Pat. No. 6,266,476 (Shie et al.) discloses a microstructure on thesurface of a polymer sheet for the diffusion of light. Themicrostructures are created by molding Fresnel lenses on the surface ofa substrate to control the direction of light output from a light sourceso as to shape the light output into a desired distribution, pattern orenvelope. While the materials disclosed in U.S. Pat. No. 6,266,476 shapeand collimate light and therefore are not efficient diffusers of lightparticularly for liquid crystal display devices.

It is known to produce transparent polymeric film having a resin coatedon one surface thereof with the resin having a surface texture. Thiskind of transparent polymeric film is made by a thermoplastic embossingprocess in which raw (uncoated) transparent polymeric film is coatedwith a molten resin, such as polyethylene. The transparent polymericfilm with the molten resin thereon is brought into contact with a chillroller having a surface pattern. Chilled water is pumped through theroller to extract heat from the resin, causing it to solidify and adhereto the transparent polymeric film. During this process the surfacetexture on the chill roller's surface is embossed into the resin coatedtransparent polymeric film. Thus, the surface pattern on the chillroller is critical to the surface produced in the resin on the coatedtransparent polymeric film.

One known prior process for preparing chill rollers involves creating amain surface pattern using a mechanical engraving process. The engravingprocess has many limitations including misalignment causing tool linesin the surface, high price, and lengthy processing. Accordingly, it isdesirable to not use mechanical engraving to manufacture chill rollers.

The U.S. Pat. No. 6,285,001 (Fleming et al) relates to an exposureprocess using excimer laser ablation of substrates to improve theuniformity of repeating microstructures on an ablated substrate or tocreate three-dimensional microstructures on an ablated substrate. Thismethod is difficult to apply to create a master chill roll tomanufacture complex random three-dimensional structures and is also costprohibitive.

In U.S. Pat. No. 6,124,974 (Burger) the substrates are made withlithographic processes. This lithography process is repeated forsuccessive photomasks to generate a three-dimensional relief structurecorresponding to the desired lenslet. This procedure to form a master tocreate three-dimensional features into a plastic film is time consumingand cost prohibitive.

PROBLEM TO BE SOLVED BY THE INVENTION

There remains a need for an improved light diffusion of imageillumination light sources to provide improved diffuse lighttransmission while simultaneously diffusing specular light sources.

SUMMARY OF THE INVENTION

The invention provides a transparent polymeric film having a top andbottom surface comprising a plurality of complex lenses on at least onesurface thereof. The invention also provides a back lighted imagingmedia, a liquid crystal display component and device, and method ofmaking them.

ADVANTAGEOUS EFFECT OF THE INVENTION

The invention provides improved light transmission while simultaneouslydiffusing specular light sources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of a complex lens formed on atransparent base material suitable for use in a liquid crystal displaydevice.

FIG. 2 illustrates a liquid crystal display device with a lightdiffuser.

DETAILED DESCRIPTION OF THE INVENTION

The invention has numerous advantages over prior practices in the art.The invention provides diffusion of specular light sources that arecommonly used in rear projection display devices such as liquid crystaldisplay devices. Further, the invention, while providing diffusion tothe light sources, has a high light transmission rate. A hightransmission rate for light diffusers is particularly important forliquid crystal display devices as a high transmission value allows theliquid crystal display to be brighter or holding the level of brightnessthe same, allows for the power consumption for the back light to bereduces therefore extending the lifetime of battery powered liquidcrystal devices that are common for note book computers. The surfacelenslet structure polymer layer of the invention can be easily changedto achieve the desired diffusion and light transmission requirements formany liquid crystal devices thus allowing the invention materials to beresponsive to the rapidly changing product requirements in the liquidcrystal display market.

The elastic modulus and scratch resistance of the diffuser is improvedover prior art cast coated polymer diffusers rendering a more robustdiffuser during the assembly operation of the liquid crystal device.These and other advantages will be apparent from the detaileddescription below.

The term “LCD” means any rear projection display device that utilizesliquid crystals to form the image. The term “diffuser” means anymaterial that is able to diffuse specular light (light with a primarydirection) to a diffuse light (light with random light direction). Theterm “light” means visible light. The term “diffuse light transmission”means the percent diffusely transmitted light at 500 nm as compared tothe total amount of light at 500 nm of the light source. The term “totallight transmission” means percentage light transmitted through thesample at 500 nm as compared to the total amount of light at 500 nm ofthe light source. This includes both spectral and diffuse transmissionof light. The term “diffuse light transmission efficiency” means theratio of % diffuse transmitted light at 500 nm to % total transmittedlight at 500 nm multiplied by a factor of 100. The term “polymeric film”means a film comprising polymers. The term “polymer” means homo- andco-polymers. The term “average”, with respect to lens size andfrequency, means the arithmetic mean over the entire film surface area.

“Transparent” means a film with total light transmission of 50% orgreater at 500 nm. “In any direction”, with respect to lensletarrangement on a film, means any direction in the x and y direction inthe plane of the film. The term “pattern” means any predeterminedarrangement of lenses whether regular or random.

Better control and management of the back light are drivingtechnological advances for liquid crystal displays (LCD). LCD screensand other electronic soft display media are back lit primarily withspecular (highly directional) fluorescent tubes. Diffusion films areused to distribute the light evenly across the entire display area andchange the light from specular to diffuse. Light exiting the liquidcrystal section of the display stack leaves as a narrow column and mustbe redispersed. Diffusers are used in this section of the display toselectively spread the light out horizontally for an enhanced viewingangle.

Diffusion is achieved by light scattering as it passes though materialswith varying indexes of refraction. This scattering produces a diffusingmedium for light energy. There is an inverse relationship betweentransmittance of light and diffusion and the optimum combination ofthese two parameters must be found for each application.

The back diffuser is placed directly in front of the light source and isused to even out the light throughout the display by changing specularlight into diffuse light. The diffusion film is made up of a pluralityof lenslets on a web material to broaden and diffuse the incoming light.Prior art methods for diffusing LCD back light include layering polymerfilms with different indexes of refraction, microvoided polymer film, orcoating the film with matte resins or beads. The role of the frontdiffuser is to broaden the light coming out of the liquid crystal (LC)with directional selectivity. The light is compressed into a tight beamto enter the LC for highest efficient and when it exits it comes out asa narrow column of light. The diffuser uses optical structures to spreadthe light selectively. Most companies form elliptical micro-lens toselectively stretch the light along one axis. Elliptically shapedpolymers in a polymer matrix and surface micro-lenses formed by chemicalor physical means also achieve this directionality. The diffusion filmof the present invention can be produced by using a conventionalfilm-manufacturing facility in high productivity.

The polymeric diffusion film has a textured surface on at least oneside, in the form of a plurality of random microlenses, or lenslets. Theterm “lenslet” means a small lens, but for the purposes of the presentdiscussion, the terms lens and lenslet may be taken to be the same. Thelenslets overlap to form complex lenses. “Complex lenses” means a majorlens having on the surface thereof multiple minor lenses. “Major lenses”mean larger lenslets in which the minor lenses are formed randomly ontop of. “Minor lenses” mean lenses smaller than the major lenses thatare formed on the major lens. The plurality of lenses of all differentsizes and shapes are formed on top of one another to create a complexlens feature resembling a cauliflower. The lenslets and complex lensesformed by the lenslets can be concave into the transparent polymericfilm or convex out of the transparent polymeric film. The term “concave”means curved like the surface of a sphere with the exterior surface ofthe sphere closest to the surface of the film. The term “convex” meanscurved like the surface of a sphere with the interior surface of thesphere closest to the surface of the film. The term “top surface” meansthe surface of the film farther from the light source. The term “bottomsurface” means the surface of the film closer to the light source.

One embodiment of the present invention could be likened to the moon'scratered surface. Asteroids that hit the moon form craters apart fromother craters, that overlap a piece of another crater, that form withinanother crater, or that engulf another crater. As more craters arecarved, the surface of the moon becomes a complexity of depressions likethe complexity of lenses formed in the transparent polymeric film.

The surface of each lenslet is a locally spherical segment, which actsas a miniature lens to alter the ray path of energy passing through thelens. The shape of each lenslet is “semi-spherical” meaning that thesurface of each lenslet is a sector of a sphere, but not necessarily ahemisphere. Its curved surface has a radius of curvature as measuredrelative to a first axis (x) parallel to the transparent polymeric filmand a radius of curvature relative to second axis (y) parallel to thetransparent polymeric film and orthogonal to the first axis (x). Thelenses in an array film need not have equal dimensions in the x and ydirections. The dimensions of the lenses, for example length in the x ory direction, are generally significantly smaller than a length or widthof the film. “Height/Diameter ratio” means the ratio of the height ofthe complex lens to the diameter of the complex lens. “Diameter” meansthe largest dimension of the complex lenses in the x and y plane. Thevalue of the height/diameter ratio is one of the main causes of theamount of light spreading, or diffusion that each complex lens creates.A small height/diameter ratio indicates that the diameter is muchgreater than the height of the lens creating a flatter, wider complexlens. A larger height/diameter value indicates a taller, skinner complexlens. The complex lenses may differ in size, shape, off-set from opticalaxis, and focal length.

The curvature, depth, size, spacing, materials of construction (whichdetermines the basic refractive indices of the polymer film and thesubstrate), and positioning of the lenslets determine the degree ofdiffusion, and these parameters are established during manufactureaccording to the invention.

The divergence of light through the lens may be termed “asymmetric”,which means that the divergence in the horizontal direction is differentfrom the divergence in the vertical direction. The divergence curve isasymmetric, or that the direction of the peak light transmission is notalong the direction θ=0°, but is in a direction non-normal to thesurface. There are least three approaches available for making the lightdisperse asymmetrically from a lenslet diffusion film, namely, changingthe dimension of the lenses in one direction relative to an orthogonaldirection, off-setting the optical axis of the lens from the center ofthe lens, and using an astigmatic lens.

The result of using a diffusion film having lenses whose optical axesare off-set from the center of the respective lenses results indispersing light from the film in an asymmetric manner. It will beappreciated, however, that the lens surface may be formed so that theoptical axis is off-set from the center of the lens in both the x and ydirections.

The lenslet structure can be manufactured on the opposite sides of thesubstrate. The lenslet structures on either side of the support can varyin curvature, depth, size, spacing, and positioning of the lenslets.

A transparent polymeric film having a top and bottom surface comprisinga plurality of convex or concave complex lenses on the surface of thetransparent polymeric film is preferred. Curved concave and convexpolymer lenses have been shown to provide very efficient diffusion oflight. Further, the polymer lenses of the invention are transparent,allowing a high transmission of light allowing the brightness of LCdisplays to emit more light.

The concave or complex lenses on the surface of the polymer film arepreferably randomly placed. Random placement of lenses increases thediffusion efficiency of the invention materials. Further, by avoiding aconcave or convex placement of lenses that ordered, undesirable opticalinterference patterns are avoided.

In an embodiment of the invention, the concave or convex lenses arelocated on both sides of the transparent polymer sheet. By placing thelenses on both sides of the transparent sheet, more efficient lightdiffusion is observed compared to the lenses of the invention on oneside. Further, the placement of the lenses on both sides of thetransparent sheet increases the focal length of the lenses furthest fromthe brightness enhancement film in a LC display device.

In one embodiment of the invention, convex lenses are present on the topsurface and convex lenses are present on the bottom surface of thetransparent polymeric film. The placement of convex lenses on both sidesof the polymer film creates stand off from other adjacent filmsproviding the necessary air gap required for efficient diffusion by thelenses.

In another embodiment of the invention, convex lenses are present on thetop surface and concave lenses are present on the bottom surface of thetransparent polymeric film. The placement of convex lenses on the topside of the polymer film creates stand off from other adjacent filmsproviding the necessary air gap required for efficient diffusion by thelenses. The placement of concave lenses on the bottom side of thepolymer film creates a surface that can be in optical contact with theadjacent films and still effectively diffuse the light.

In another embodiment of the invention, concave lenses are present onthe top surface and concave lenses are present on the bottom surface ofthe transparent polymeric film. The placement of concave lenses on bothsides of the polymer film creates a surface that can be in opticalcontact with the adjacent films on either side and still effectivelydiffuse the light.

In another embodiment of the invention, concave lenses are present onthe top surface and convex lenses are present on the bottom surface ofthe transparent polymeric film. The placement of concave lenses on thetop side of the polymer film creates a surface that can be in opticalcontact with the adjacent films and still effectively diffuse the light.The placement of convex lenses on the bottom side of the polymer filmcreates stand off from other adjacent films providing the necessary airgap required for efficient diffusion by the lenses.

Preferably, the concave or convex lenses have an average frequency inany direction of between 4 and 250 complex lenses/mm. When a film has anaverage of 285 complex lenses/mm creates the width of the lensesapproach the wavelength of light. The lenses will impart a color to thelight passing through the lenses and change the color temperature of thedisplay. Less than 4 lenses/mm Creates lenses that are too large andtherefore diffuse the light less efficiently. Concave or convex lenseswith an average frequency in any direction of between 22 and 66 complexlenses/mm are most preferred. It has been shown that an averagefrequency of between 22 and 6 complex lenses provide efficient lightdiffusion and can be efficiently manufactured utilizing cast coatedpolymer against a randomly patterned roll.

The preferred transparent polymeric film has concave or convex lenses atan average width between 3 and 60 microns in the x and y direction. Whenlenses have sizes below 1 micron the lenses impart a color shift in thelight passing through because the lenses dimensions are on the order ofthe wavelength of light. When the lenses have an average width in the xor y direction of more than 68 microns, the lenses is too large todiffuse the light efficiently. More preferred, the concave or convexlenses at an average width between 15 and 40 microns in the x and ydirection. This size lenses has been shown to create the most efficientdiffusion.

The concave or convex complex lenses comprising minor lenses wherein thediameter of the smaller lenses is preferably less than 80%, on average,the diameter of the major lens. When the diameter of the minor lensexceeds 80% of the major lens, the diffusion efficiency is decreasedbecause the complexity of the lenses is reduced.

The concave or convex complex lenses comprising minor lenses wherein thewidth in the x and y direction of the smaller lenses is preferablybetween 2 and 20 microns. When minor lenses have sizes below 1 micronthe lenses impart a color shift in the light passing through because thelenses dimensions are on the order of the wavelength of light. When theminor lenses have sizes above 25 microns, the diffusion efficiency isdecreased because the complexity of the lenses is reduced. Mostpreferred are the minor lenses having a width in the x and y directionbetween 3 and 8 microns. This range has been shown to create the mostefficient diffusion.

Preferably, the concave or convex complex lenses comprise an olefinrepeating unit. Polyolefins are low in cost and high in lighttransmission. Further, polyolefin polymers are efficiently meltextrudable and therefore can be used to create light diffusers in rollform.

In another embodiment of the invention, the concave or convex complexlenses comprise a carbonate repeating unit. Polycarbonates have highoptical transmission values that allows for high light transmission anddiffusion. High light transmission provides for a brighter LC devicethan diffusion materials that have low light transmission values.

In another embodiment of the invention, the concave or convex complexlenses comprise an ester repeating unit. Polyesters are low in cost andhave good strength and surface properties. Further, polyester polymer isdimensionally stable at temperatures between 80 and 200 degrees C. andtherefore can withstand the heat generated by display light sources.

Preferably, the transparent polymeric film wherein the polymeric filmcomprises an ester repeating unit. Polyesters are low in cost and havegood strength and surface properties. Further, polyester polymer film isdimensionally stable over the current range of temperatures encounteredin enclosed display devices. Polyester polymer easily fractures allowingfor die cutting of diffuser sheets for insertion into display devices.

In another embodiment of the invention, the transparent polymeric filmwherein the polymeric film comprises a carbonate repeating unit.Polycarbonates have high optical transmission values compared topolyolefin polymers and therefore can improve the brightness of displaydevices.

In another embodiment of the invention, the transparent polymeric filmwherein the polymeric film comprises an olefin repeating unit.Polyolefins are low in cost and have good strength and surfaceproperties.

In another embodiment of the invention, the transparent polymeric filmwherein the polymeric film comprises a tri acetyl cellulose. Tri acetylcellulose has both high optical transmission and low opticalbirefringence allowing the diffuser of the invention to both diffuselight and reduce unwanted optical patterns.

The preferred diffuse light transmission of the diffuser material of theinvention is greater than 50%. Diffuser light transmission less than 45%does not let a sufficient quantity of light pass through the diffuser,thus making the diffuser inefficient. A more preferred diffuse lighttransmission of the lenslet film is greater than between 80 and 95%. An80% diffuse transmission allows the LC device to improve battery lifeand increase screen brightness. The most preferred diffuse transmissionof the transparent polymeric film is greater than 92%. A diffusetransmission of 92% allows diffusion of the back light-source andmaximizes the brightness of the LC device significant improving theimage quality of an LC device for outdoor use where the LC screen mustcompete with natural sunlight.

Preferably, the concave or convex lenses are semi-spherical meaning thatthe surface of each lenslet is a sector of a sphere, but not necessarilya hemisphere. This provides excellent even diffusion over the x y plane.The semi-spherical shaped lenses scatter the incident light uniformly,ideal for a backlit display application where the display area need tobe lit uniformly.

In another embodiment of the invention, the concave or convex lenses areaspherical meaning that width of the lenses differ in the x and ydirection. This scatters light selectively over the x y plane. Forexample, a particular x y aspect ratio might produce an ellipticalscattering pattern. This would be useful in the front of a LC display,spreading the light more in the horizontal direction than the verticaldirection for increased viewing angle.

The convex or concave lenses preferably have a height/diameter ratio ofbetween 0.03 to 1.0. A height/diameter ratio of less than 0.01 (verywide and shallow lenses) limits diffusivity because the lenses do nothave enough curvature to efficiently spread the light. A height/diameterratio of greater than 2.5 creates lenses where the angle between theside of the lenses and the substrate is large. This causes internalreflection limiting the diffusion capability of the lenses. Mostpreferred is a height/diameter of the convex or concave lenses ofbetween 0.25 to 0.48. It has been proven that the most efficientdiffusion occurs in this range.

The number of minor lenses per major lens is preferably between 2 and60. When a major lens has one or no minor lenses, its complexity isreduced and therefore it does not diffuse as efficiently. When a majorlens has more than 70 minor lens contained on it, the width of some ofthe minor lens approaches the wavelength of light and imparts a color tothe light transmitted. Most preferred is 5 to 18 minor lenses per majorlens. This range has been shown to produce the most efficient diffusion.

The thickness of the transparent polymeric film preferably is less than250 micrometers or more preferably between 12.5 and 50 micrometers.Current design trends for LC devices are toward lighter and thinnerdevices. By reducing the thickness of the light diffuser to less than250 micrometers, the LC devices can be made lighter and thinner.Further, by reducing the thickness of the light diffuser, brightness ofthe LC device can be improved by reducing light transmission. The morepreferred thickness of the light diffuser is between 12.5 and 50micrometers which further allows the light diffuser to be convienentlycombined with a other optical materials in an LC device such asbrightness enhancement films. Further, by reducing the thickness of thelight diffuser, the materials content of the diffuser is reduced.

Since the thermoplastic light diffuser of the invention typically isused in combination with other optical web materials, a light diffuserwith an elastic modulus greater than 500 MPa is preferred. An elasticmodulus greater than 500 MPa allows for the light diffuser to belaminated with a pressure sensitive adhesive for combination with otheroptical webs materials. Further, because the light diffuser ismechanically tough, the light diffuser is better able to with stand therigors of the assembly process compared to prior art cast diffusionfilms which are delicate and difficult to assemble.

FIG. 1 illustrates a cross section of a complex lens formed on atransparent base material suitable for use in a liquid crystal displaydevice. Light diffusion film 12 comprises transparent polymer base 20,onto which convex major lens 22 is present on the surface of transparentpolymer base 26. Minor lenses 24 are present on the surface of the majorlens 22. The invention comprises a plurality of minor lenses 24 on thesurface of the major lens 22 thus forming a complex lens. The lightdiffusion film of the invention contains many diffusion surfaces fromboth the major lens 22 and the minor lenses 24.

FIG. 2 illustrates a liquid crystal display device with a lightdiffuser. Visible light source 18 is illuminated and light is guidedinto light guide 2. Lamp reflector 4 is used to direct light energy intothe light guide 2, represented by an acrylic box. Reflection tape 6,reflection tape 10 and reflection film 8 are utilized to keep lightenergy from exiting the light guide 2 in an unwanted direction. Lightdiffusion film 12 in the form of a transparent polymeric film isutilized to diffuse light energy exiting the light guide in a directionperpendicular to the light diffuser. Brightness enhancement film 14 isutilized to focus the light energy into polarization film 16. The lightdiffusion film 12 is in contact with brightness enhancement film 14.

Polymer sheet for the transparent polymeric film comprising a pluralityof convex and/or concave complex lenses on a surface thereof aregenerally dimensionally stable, optically clear and contain a smoothsurface. Biaxially oriented polymer sheets are preferred as they arethin and are higher in elastic modulus compared to cast coated polymersheets. Biaxially oriented sheets are conveniently manufactured byco-extrusion of the sheet, which may contain several layers, followed bybiaxial orientation. Such biaxially oriented sheets are disclosed in,for example, U.S. Pat. No. 4,764,425.

Suitable classes of thermoplastic polymers for the transparent polymericfilm include polyolefins, polyesters, polyamides, polycarbonates,cellulosic esters, polystyrene, polyvinyl resins, polysulfonamides,polyethers, polyimides, polyvinylidene fluoride, polyurethanes,polyphenylenesulfides, polytetrafluoroethylene, polyacetals,polysulfonates, polyester ionomers, and polyolefin ionomers. Copolymersand/or mixtures of these polymers can be used.

Polyolefins particularly polypropylene, polyethylene, polymethylpentene,and mixtures thereof are preferred. Polyolefin copolymers, includingcopolymers of propylene and ethylene such as hexene, butene and octeneare also preferred. Polypropylenes are most preferred because they arelow in cost and have good strength and surface properties.

Preferred polyesters for the transparent polymeric film of the inventioninclude those produced from aromatic, aliphatic or cycloaliphaticdicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclicglycols having from 2-24 carbon atoms. Examples of suitable dicarboxylicacids include terephthalic, isophthalic, phthalic, naphthalenedicarboxylic acid, succinic, glutaric, adipic, azelaic, sebacic,fumaric, maleic, itaconic, 1,4-cyclohexanedicarboxylic,sodiosulfoisophthalic and mixtures thereof. Examples of suitable glycolsinclude ethylene glycol, propylene glycol, butanediol, pentanediol,hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, otherpolyethylene glycols and mixtures thereof. Such polyesters are wellknown in the art and may be produced by well known techniques, e.g.,those described in U.S. Pat. No. 2,465,319 and U.S. Pat. No. 2,901,466.Preferred continuous matrix polyesters are those having repeat unitsfrom terephthalic acid or naphthalene dicarboxylic acid and at least oneglycol selected from ethylene glycol, 1,4-butanediol and1,4-cyclohexanedimethanol. Poly(ethylene terephthalate), which may bemodified by small amounts of other monomers, is especially preferred.Other suitable polyesters include liquid crystal copolyesters formed bythe inclusion of suitable amount of a co-acid component such as stilbenedicarboxylic acid. Examples of such liquid crystal copolyesters arethose disclosed in U.S. Pat. Nos. 4,420,607, 4,459,402 and 4,468,510.

Useful polyamides for the transparent polymeric film include nylon 6,nylon 66, and mixtures thereof. Copolymers of polyamides are alsosuitable continuous phase polymers. An example of a useful polycarbonateis bisphenol-A polycarbonate. Cellulosic esters suitable for use as thecontinuous phase polymer of the composite sheets include cellulosenitrate, cellulose triacetate, cellulose diacetate, cellulose acetatepropionate, cellulose acetate butyrate, and mixtures or copolymersthereof. Useful polyvinyl resins include polyvinyl chloride, poly(vinylacetal), and mixtures thereof. Copolymers of vinyl resins can also beutilized.

The complex lenses of the invention preferably comprise polymers.Polymers are preferred as they are generally lower in cost compared toprior art glass lenses, have excellent optical properties and can beefficiently formed into lenses utilizing known processes such as meltextrusion, vacuum forming and injection molding. Preferred polymers forthe formation of the complex lenses include polyolefins, polyesters,polyamides, polycarbonates, cellulosic esters, polystyrene, polyvinylresins, polysulfonamides, polyethers, polyimides, polyvinylidenefluoride, polyurethanes, polyphenylenesulfides, polytetrafluoroethylene,polyacetals, polysulfonates, polyester ionomers, and polyolefinionomers. Copolymers and/or mixtures of these polymers to improvemechanical or optical properties can be used. Preferred polyamides forthe transparent complex lenses include nylon 6, nylon 66, and mixturesthereof. Copolymers of polyamides are also suitable continuous phasepolymers. An example of a useful polycarbonate is bisphenol-Apolycarbonate. Cellulosic esters suitable for use as the continuousphase polymer of the complex lenses include cellulose nitrate, cellulosetriacetate, cellulose diacetate, cellulose acetate propionate, celluloseacetate butyrate, and mixtures or copolymers thereof. Preferredpolyvinyl resins include polyvinyl chloride, poly(vinyl acetal), andmixtures thereof. Copolymers of vinyl resins can also be utilized.Preferred polyesters for the complex lens of the invention include thoseproduced from aromatic, aliphatic or cycloaliphatic dicarboxylic acidsof 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24carbon atoms. Examples of suitable dicarboxylic acids includeterephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid,succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic,1,4-cyclohexanedicarboxylic, sodiosulfoisophthalic and mixtures thereof.Examples of suitable glycols include ethylene glycol, propylene glycol,butanediol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol,diethylene glycol, other polyethylene glycols and mixtures thereof.

Addenda is preferably added to a polyester skin layer to change thecolor of the imaging element. An addenda of this invention that could beadded is an optical brightener. An optical brightener is substantiallycolorless, fluorescent, organic compound that absorbs ultraviolet lightand emits it as visible blue light. Examples include but are not limitedto derivatives of 4,4′-diaminostilbene-2,2′-disulfonic acid, coumarinderivatives such as 4-methyl-7-diethylaminocoumarin, 1-4-Bis(O-Cyanostyryl) Benzol and 2-Amino-4-Methyl Phenol. An unexpecteddesirable feature of this efficient use of optical brightener. Becausethe ultraviolet source for a transmission display material is on theopposite side of the image, the ultraviolet light intensity is notreduced by ultraviolet filters common to imaging layers. The result isless optical brightener is required to achieve the desired backgroundcolor.

The diffuser sheets may be coated or treated before or afterthermoplastic lenslet casting with any number of coatings which may beused to improve the properties of the sheets including printability, toprovide a vapor barrier, to make them heat sealable, or to improveadhesion. Examples of this would be acrylic coatings for printability,coating polyvinylidene chloride for heat seal properties. Furtherexamples include flame, plasma or corona discharge treatment to improveprintability or adhesion.

The diffuser sheets of the present invention may be used in combinationwith one or more layers selected from an optical compensation film, apolarizing film and a substrate constitution a liquid crystal layer. Thediffusion film of the present invention is preferably used by acombination of diffusion film/polarizing film/optical compensation filmin that order. In the case of using the above films in combination in aliquid crystal display device, the films could be bonded with each othere.g. through a tacky adhesive for minimizing the reflection loss, etc.The tacky adhesive is preferably those having a refractive index closeto that of the oriented film to suppress the interfacial reflection lossof light.

The lenslet diffuser film may also be used in conjunction with anotherlight diffuser, for example a bulk diffuser, a lenticular layer, abeaded layer, a surface diffuser, a holographic diffuser, amicro-structured diffuser, another lens array, or various combinationsthereof. The lenslet diffuser film disperses, or diffuses, the light,thus destroying any diffraction pattern that may arise from the additionof an ordered periodic lens array. The lenslet diffuser film may bepositioned before or after any diffuser or lens array.

The diffusion sheet of the present invention may be used in combinationwith a film or sheet made of a transparent polymer. Examples of suchpolymer are polyesters such as polycarbonate, polyethyleneterephthalate, polybutylene terephthalate and polyethylene naphthalate,acrylic polymers such as polymethyl methacrylate, and polyethylene,polypropylene, polystyrene, polyvinyl chloride, polyether sulfone,polysulfone, polyacrylate and triacetyl cellulose. The bulk diffuserlayer may be mounted to a glass sheet for support.

The transparent polymeric film of the invention can also include, inanother aspect, one or more optical coatings to improve opticaltransmission through one or more lenslet channels. It is often desirableto coat a diffuser with a layer of an anti-reflective (AR) coating inorder to raise the efficiency of the diffuser.

The diffuser sheet of the present invention may be incorporated withe.g. an additive or a lubricant such as silica for improving thesurface-slipperiness of the film within a range not to deteriorate theoptical characteristics to vary the light-scattering property with anincident angle. Examples of such additive are organic solvents such asxylene, alcohols or ketones, fine particles of an acrylic resin,silicone resin or Δ metal oxide or a filler.

The lenslet diffuser film of the present invention usually has opticalanisotropy. The web material and the casted thermoplastic resin aregenerally optically anisotropic materials exhibiting optical anisotropyhaving an optic axis in the drawing direction. The optical anisotropy isexpressed by the product of the film thickness d and the birefringenceΔn which is a difference between the refractive index in the slow opticaxis direction and the refractive index in the fast optic axis directionin the plane of the film, i.e. Δn*d (retardation). The orientationdirection coincides with the drawing axis in the film of the presentinvention. The drawing axis is the direction of the slow optic axis inthe case of a thermoplastic polymer having a positive intrinsicbirefringence and is the direction of the fast optic axis for athermoplastic polymer having a negative intrinsic birefringence. Thereis no definite requirement for the necessary level of the value of Δn*dsince the level depends upon the application of the film.

In the manufacturing process for this invention, preferred lens polymersare melt extruded from a slit die. In general, a T die or a coat hangerdie are preferably used. The process involves extruding the polymer orpolymer blend through a slit die and rapidly quenching the extruded webupon a chilled casting drum with the preferred lens geometry so that thelens polymer component of the transparent sheet are quenched below theirglass solidification temperature and retain the shape of the diffusionlens.

A method of fabricating a diffusion film assembly was developed. Thepreferred approach comprises the steps of providing a positive masterchill roll having a plurality of complex lenses. The diffusion film isreplicated from the master chill roller by casting a molten polymericmaterial to the face of the chill roll and transferring the polymericmaterial with lenslet structures onto a transparent polymeric film.

A chill roller is manufactured by a process including the steps ofelectroplating a layer of cooper onto the surface of a roller, and thenabrasively blasting the surface of the copper layer with beads, such asglass or silicon dioxide, to create a surface texture with hemisphericalfeatures. The resulting blasted surface is bright nickel electroplatedor chromed to a depth that results in a surface texture with thefeatures either concave into the roll or convex out of the roll. Becauseof the release characteristics of the chill roll surface, the resin willnot adhere to the surface of the roller.

The bead blasting operation is carried out using an automated directpressure system in which the nozzle feed rate, nozzle distance from theroller surface, the roller rotation rate during the blasting operationand the velocity of the particles are accurately controlled to createthe desired lenslet structure.

The number of features in the chill roll per area is determined by thebead size and the pattern depth. Larger bead diameters and deeperpatterns result in fewer numbers of features in a given area. Thereforethe number of features is inherently determined by the bead size and thepattern depth.

The complex lenses of the invention may also be manufactured by vacuumforming around a pattern, injection molding the lenses and embossinglenses in a polymer web. While these manufacturing techniques do yieldacceptable lenses capable of efficiently diffusing light, melt castcoating polymer onto a patterned roll and subsequent transfer onto atransparent polymer web allows for the lenses of the invention to beformed into rolls thereby lowering the manufacturing cost for thediffusion lenses. Further, cast coating polymer has been shown to moreefficiently replicate the desired complex lens geometry compared toembossing and vacuum forming.

The invention may be used in conjunction with any liquid crystal displaydevices, typical arrangements of which are described in the following.Liquid crystals (LC) are widely used for electronic displays. In thesedisplay systems, an LC layer is situated between a polarizer layer andan analyzer layer and has a director exhibiting an azimuthal twistthrough the layer with respect to the normal axis. The analyzer isoriented such that its absorbing axis is perpendicular to that of thepolarizer. Incident light polarized by the polarizer passes through aliquid crystal cell is affected by the molecular orientation in theliquid crystal, which can be altered by the application of a voltageacross the cell. By employing this principle, the transmission of lightfrom an external source, including ambient light, can be controlled. Theenergy required to achieve this control is generally much less than thatrequired for the luminescent materials used in other display types suchas cathode ray tubes. Accordingly, LC technology is used for a number ofapplications, including but not limited to digital watches, calculators,portable computers, electronic games for which light weight, low powerconsumption and long operating life are important features.

Active-matrix liquid crystal displays (LCDs) use thin film transistors(TFTs) as a switching device for driving each liquid crystal pixel.These LCDs can display higher-definition images without cross talkbecause the individual liquid crystal pixels can be selectively driven.Optical mode interference (OMI) displays are liquid crystal displays,which are “normally white,” that is, light is transmitted through thedisplay layers in the off state. Operational mode of LCD using thetwisted nematic liquid crystal is roughly divided into a birefringencemode and an optical rotatory mode. “Film-compensated super-twistednematic” (FSTN) LCDs are normally black, that is, light transmission isinhibited in the off state when no voltage is applied. OMI displaysreportedly have faster response times and a broader operationaltemperature range.

Ordinary light from an incandescent bulb or from the sun is randomlypolarized, that is, it includes waves that are oriented in all possibledirections. A polarizer is a dichroic material that functions to converta randomly polarized (“unpolarized”) beam of light into a polarized oneby selective removal of one of the two perpendicular plane-polarizedcomponents from the incident light beam. Linear polarizers are a keycomponent of liquid-crystal display (LCD) devices.

There are several types of high dichroic ratio polarizers possessingsufficient optical performance for use in LCD devices. These polarizersare made of thin sheets of materials which transmit one polarizationcomponent and absorb the other mutually orthogonal component (thiseffect is known as dichroism). The most commonly used plastic sheetpolarizers are composed of a thin, uniaxially-stretched polyvinylalcohol (PVA) film which aligns the PVA polymer chains in a more-or-lessparallel fashion. The aligned PVA is then doped with iodine molecules ora combination of colored dichroic dyes (see, for example, EP 0 182 632A2, Sumitomo Chemical Company, Limited) which adsorb to and becomeuniaxially oriented by the PVA to produce a highly anisotropic matrixwith a neutral gray coloration. To mechanically support the fragile PVAfilm it is then laminated on both sides with stiff layers of triacetylcellulose (TAC), or similar support.

Contrast, color reproduction, and stable gray scale intensities areimportant quality attributes for electronic displays, which employliquid crystal technology. The primary factor limiting the contrast of aliquid crystal display is the propensity for light to “leak” throughliquid crystal elements or cell, which are in the dark or “black” pixelstate. Furthermore, the leakage and hence contrast of a liquid crystaldisplay are also dependent on the angle from which the display screen isviewed. Typically the optimum contrast is observed only within a narrowviewing angle centered about the normal incidence to the display andfalls off rapidly as the viewing angle is increased. In color displays,the leakage problem not only degrades the contrast but also causes coloror hue shifts with an associated degradation of color reproduction. Inaddition to black-state light leakage, the narrow viewing angle problemin typical twisted nematic liquid crystal displays is exacerbated by ashift in the brightness-voltage curve as a function of viewing anglebecause of the optical anisotropy of the liquid crystal material.

The transparent polymeric film of the present invention can even out theluminance when the film is used as a light-scattering film in abacklight system. Back-lit LCD display screens, such as are utilized inportable computers, may have a relatively localized light source (ex.fluorescent light) or an array of relatively localized light sourcesdisposed relatively close to the LCD screen, so that individual “hotspots” corresponding to the light sources may be detectable. Thediffuser film serves to even out the illumination across the display.The liquid crystal display device includes display devices having acombination of a driving method selected from e.g. active matrix drivingand simple matrix drive and a liquid crystal mode selected from e.g.twist nematic, supertwist nematic, ferroelectric liquid crystal andantiferroelectric liquid crystal mode, however, the invention is notrestricted by the above combinations. In a liquid crystal displaydevice, the oriented film of the present invention is necessary to bepositioned in front of the backlight. The lenslet diffuser film of thepresent invention can even the lightness of a liquid crystal displaydevice across the display because the film has excellentlight-scattering properties to expand the light to give excellentvisibility in all directions. Although the above effect can be achievedeven by the single use of such lenslet diffuser film, plural number offilms may be used in combination. The homogenizing lenslet diffuser filmmay be placed in front of the LCD material in a transmission mode todisburse the light and make it much more homogenous. The presentinvention has a significant use as a light source destructuring device.In many applications, it is desirable to eliminate from the output ofthe light source itself the structure of the filament which can beproblematic in certain applications because light distributed across thesample will vary and this is undesirable. Also, variances in theorientation of a light source filament or arc after a light source isreplaced can generate erroneous and misleading readings. A homogenizinglenslet diffuser film of the present invention placed between the lightsource and the detector can eliminate from the output of the lightsource any trace of the filament structure and therefore causes ahomogenized output which is identical from light source to light source.

The lenslet diffuser films may be used to control lighting for stages byproviding pleasing homogenized light that is directed where desired. Instage and television productions, a wide variety of stage lights must beused to achieve all the different effects necessary for proper lighting.This requires that many different lamps be used which is inconvenientand expensive. The films of the present invention placed over a lamp cangive almost unlimited flexibility dispersing light where it is needed.As a consequence, almost any object, moving or not, and of any shape,can be correctly illuminated.

The reflection film formed by applying a reflection layer composed of ametallic film, etc., to the lenslet diffuser film of the presentinvention can be used e.g. as a retroreflective member for a trafficsign. It can be used in a state applied to a car, a bicycle, person,etc.

The lenslet diffuser films of the present invention may also be used inthe area of law enforcement and security systems to homogenize theoutput from laser diodes (LDs) or light emitting diodes (LEDs) over theentire secured area to provide higher contrasts to infrared (IR)detectors. The films of the present invention may also be used to removestructure from devices using LED or LD sources such as in bank notereaders or skin treatment devices. This leads to greater accuracy.

Fiber-optic light assemblies mounted on a surgeon's headpiece can castdistracting intensity variations on the surgical field if one of thefiber-optic elements breaks during surgery. A lenslet diffuser film ofthe present invention placed at the ends of the fiber bundle homogenizeslight coming from the remaining fibers and eliminates any trace of thebroken fiber from the light cast on the patient. A standard ground glassdiffuser would not be as effective in this use due to significantback-scatter causing loss of throughput.

The lenslet diffuser films of the present invention can also be used tohomogeneously illuminate a sample under a microscope by destructuringthe filament or arc of the source, yielding a homogeneously illuminatedfield of view. The films may also be used to homogenize the variousmodes that propagate through a fiber, for example, the light output froma helical-mode fiber.

The lenslet diffuser films of the present invention also havesignificant architectural uses such as providing appropriate light forwork and living spaces. In typical commercial applications, inexpensivetransparent polymeric diffuser films are used to help diffuse light overthe room. A homogenizer of the present invention which replaces one ofthese conventional diffusers provides a more uniform light output sothat light is diffused to all angles across the room evenly and with nohot spots.

The lenslet diffuser films of the present invention may also be used todiffuse light illuminating artwork. The transparent polymeric filmdiffuser provides a suitable appropriately sized and directed aperturefor depicting the artwork in a most desirable fashion.

Further, the lenslet diffuser film of the present invention can be usedwidely as a part for an optical equipment such as a displaying device.For example, it can be used as a light-reflection plate laminated with areflection film such as a metal film in a reflective liquid crystaldisplay device or a front scattering film directing the film to thefront-side (observer's side) in the case of placing the metallic film tothe back side of the device (opposite to the observer), in addition tothe aforementioned light-scattering plate of a backlight system of aliquid crystal display device. The lenslet diffuser film of the presentinvention can be used as an electrode by laminating a transparentconductive layer composed of indium oxide represented by ITO film. Ifthe material is to be used to form a reflective screen, e.g. frontprojection screen, a light-reflective layer is applied to thetransparent polymeric film diffuser.

Another application for the transparent polymeric diffuser film is arear projection screen, where it is generally desired to project theimage from a light source onto a screen over a large area. The viewingangle for a television is typically smaller in the vertical directionthan in the horizontal direction. The diffuser acts to spread the lightto increase viewing angle.

Diffusion film samples were measured with the Hitachi U4001 UV/Vis/NIRspectrophotometer equipped with an integrating sphere. The totaltransmittance spectra were measured by placing the samples at the beamport with the front surface with complex lenses towards the integratingsphere. A calibrated 99% diffusely reflecting standard (NIST-traceable)was placed at the normal sample port. The diffuse transmittance spectrawere measured in like manner, but with the 99% tile removed. The diffusereflectance spectra were measured by placing the samples at the sampleport with the coated side towards the integrating sphere. In order toexclude reflection from a sample backing, nothing was placed behind thesample. All spectra were acquired between 350 and 800 nm. As the diffusereflectance results are quoted with respect to the 99% tile, the valuesare not absolute, but would need to be corrected by the calibrationreport of the 99% tile.

Percentage total transmitted light refers to percent of light that istransmitted though the sample at all angles. Diffuse transmittance isdefined as the percent of light passing though the sample excluding a2.5 degree angle from the incident light angle. The diffuse lighttransmission is the percent of light that is passed through the sampleby diffuse transmittance. Diffuse reflectance is defined as the percentof light reflected by the sample. The percentages quoted in the exampleswere measured at 500 nm. These values may not add up to 100% due toabsorbencies of the sample or slight variations in the sample measured.

Embodiments of the invention may provide not only improved lightdiffusion and transmission but also a diffusion film of reducedthickness, and that has reduced light scattering tendencies.

The entire contents of the patents and other publications referred to inthis specification are incorporated herein by reference.

EXAMPLES

In this example, complex light diffusion lenses of the invention werecreated by extrusion casting a extrusion grade polyolefin polymeragainst a pattered chill roll containing the complex lens geometry. Thepatterned polyolefin polymer, in the form the complex lens was thentransferred to a polyester web material thereby forming a light diffuserwith complex surface lenses. This example will show that complex surfacelenses formed on a transparent polymer web material provide exceptionallight diffusion compared to random single polymer lenses formed on thesurface of a polymer web and a prior art light diffuser utilizing adispersion of spherical beads in an acrylic matrix. Further, it will beobvious that the light diffuser will be low in cost and have mechanicalproperties that allows for insertion into LC devices.

Two patterned chill rolls (complex lens and a single lens geometry) weremanufactured by a process including the steps of electroplating a layerof cooper onto the surface of a roller, and then abrasively blasting thesurface of the copper layer with glass beads to create a surface texturewith hemispherical features. The resulting blasted surface was brightnickel electroplated to a depth that results in a surface texture withthe features either concave into the roll or convex out of the roll. Thebead blasting operation was carried out using an automated directpressure system in which the nozzle feed rate, nozzle distance from theroller surface, the roller rotation rate during the blasting operationand the velocity of the particles are accurately controlled to createthe desired complex lens structure. The number of features in the chillroll per area is determined by the bead size and the pattern depth.Larger bead diameters and deeper patterns result in fewer numbers offeatures in a given area.

The complex lens patterned roll was manufactured by starting with asteel roll blank and grit blasted with size 14 grit at a pressure of 447MPa. The roll was then chrome platted. The resulting complex lenses onthe surface of the roll were convex. The single lens patterned roll(control) was manufactured by starting with a copper roll blank and gritblasted with size 14 spherical grit at a pressure of 310 MPa. Theresulting single lenses on the surface of the roll were concave.

The two patterned chill rolls were utilized to create light diffusionsheets by extrusion coating a polyolefin polymer from a coat hanger slotdie comprising substantially 96.5% LDPE (Eastman Chemical grade D4002P),3% Zinc Oxide and 0.5% of calcium stearate onto a 100 micrometertransparent oriented web polyester web with a % light transmission of97.2%. The polyolefin cast coating coverage was 25.88 g/m².

The invention materials containing complex lenses had randomlydistributed lenses comprising a major lens with an average diameter of27.1 micrometers and minor lenses on the surface of the major lenseswith an average diameter of 6.7 micrometers. The average minor to majorlens ratio was 17.2 to 1. The control diffusion sheet comprisingrandomly distributed single lenses with an average diameter of 25.4micrometers. The structure of the cast coated diffusion sheets is asfollows,

Formed polyolefin lenses Transparent polyester base

The two diffusion sheets containing formed polymer lenses from above(invention and control) and a prior polymer light diffuser containing 8micrometers polymer beads in an acrylic binder layer coated on apolyester web material were measured for % light transmission, % diffuselight transmission, % specular light transmission and % diffusereflectance.

Diffusion film samples were measured with the Hitachi U4001 UV/Vis/NIRspectrophotometer equipped with an integrating sphere. The totaltransmittance spectra were measured by placing the samples at the beamport with the front surface with complex lenses towards the integratingsphere. A calibrated 99% diffusely reflecting standard (NIST-traceable)was placed at the normal sample port. The diffuse transmittance spectrawere measured in like manner, but with the 99% tile removed. The diffusereflectance spectra were measured by placing the samples at the sampleport with the coated side towards the integrating sphere. In order toexclude reflection from a sample backing, nothing was placed behind thesample. All spectra were acquired between 350 and 800 nm. As the diffusereflectance results are quoted with respect to the 99% tile, the valuesare not absolute, but would need to be corrected by the calibrationreport of the 99% tile.

Percentage total transmitted light refers to percent of light that istransmitted though the sample at all angles. Diffuse transmittance isdefined as the percent of light passing though the sample excluding a2.5 degree angle from the incident light angle. The diffuse lighttransmission is the percent of light that is passed through the sampleby diffuse transmittance. Diffuse reflectance is defined as the percentof light reflected by the sample. The percentages quoted in the exampleswere measured at 500 nm. These values may not add up to 100% due toabsorbencies of the sample or slight variations in the sample measured.

The measured values for the invention, control and prior art materialsare listed in Table 1 below.

TABLE 1 1 2 3 Invention Control Control Sample (Complex Lens) (SingleLens) (Prior Art) Total transmission 91.7 87.4 66.7 measured at 500 nmDiffuse transmission 85.2 59.0 65.7 measured at 500 nm Spectraltransmission 6.5 28.4 1.0 measured at 500 nm Diffuse reflectance 7.6 5.733.3 measured at 500 nm

As the data above clearly indicates, complex polymer lenses formed onthe surface of a transparent polymer provide excellent light diffusionand % transmission allowing for brighter liquid crystal display devices.The diffuse light transmission of 85.2% for the invention materials issignificantly better than both the single lens (59.0%) and the prior artmaterials (65.7%). The complex lens of the invention providessignificantly more curved surface area for transmitted light diffusioncompared to a single lens (one curved surface) and the prior artmaterials (one curved surface). Diffuse light transmission is importantfactor in the quality of a LC device in that the diffusion sheet mustmask the pattern of the light guide common to LC devices. The totallight transmission of the invention of 91.7% is significantly improvedover the single lens (59.0) and the prior art materials. By providing alens that reduces internal scattering and reflection back toward thesource, the invention materials allow for 91.7% of the light energy topass through the diffuser resulting in a brighter liquid crystaldisplay.

Integrating all of the measurements in Table 1, sample one combined hightotal transmission with high diffuse light transmission. This created afilm that masked the pattern of the light guide while allowing most ofthe light through the film to enable a brighter LC display. Sample twohad a high transmission value creating a bright LC display, but lowdiffuse transmission value so the pattern of the light guide could beseen through the display. In sample three, most of the light exiting thefilm was diffuse thus masking the pattern of the light guide. Though thelight exiting was almost totally diffuse, the total transmissionmeasurement was low blocking light and creating an unacceptably darkdisplay. Light through sample three was also wasted by a large percentof reflection.

Further, because the invention materials were constructed on a orientedpolyester base, the materials have a higher elastic modulus compared tocast diffuser sheets. The oriented polymer base of the example allow forthe light diffuser to be thin and therefore cost efficient and light asthe materials content of the example materials is reduced compared toprior art materials.

While this example was primarily directed toward the use ofthermoplastic light diffusion materials for LC devices, the materials ofthe invention have value in other diffusion applications such as backlight display, imaging elements containing a diffusion layer, a diffuserfor specular home lighting and privacy screens, image capture diffusionlenses and greenhouse light diffusion.

PARTS LIST

2. Light guide

4. Lamp Reflector

6. Reflection tape

8. Reflection film

10. Reflection tape

12. Light diffusion film

14. Brightness enhancement film

16. Polarization film

18. Visible light source

20. Transparent polymer base

22. Major lens

24. Minor lens

26. Surface of transparent polymer base

What is claimed is:
 1. A transparent polymeric film having a top andbottom surface comprising a plurality of complex lenses on at least onesurface thereof.
 2. The transparent polymeric film of claim 1 whereinthe complex lenses are randomly distributed on the surface.
 3. Thetransparent polymeric film of claim 1 wherein the complex lenses arepresent on both the top and bottom surfaces of the transparent polymericfilm.
 4. The transparent polymeric film of claim 3 wherein convexcomplex lenses are present on the top surface of the transparentpolymeric film and convex complex lenses are present on the bottomsurface of the transparent polymeric film.
 5. The transparent polymericfilm of claim 3 wherein convex complex lenses are present on the topsurface of the transparent polymeric film and concave complex lenses arepresent on the bottom surface of the transparent polymeric film.
 6. Thetransparent polymeric film of claim 3 wherein concave complex lenses arepresent on the top surface of the transparent polymeric film and concavecomplex lenses are present on the bottom surface of the transparentpolymeric film.
 7. The transparent polymeric film of claim 3 whereinconcave complex lenses are present on the top surface of the transparentpolymeric film and convex complex lenses are present on the bottomsurface of the transparent polymeric film.
 8. The transparent polymericfilm of claim 1 wherein the complex lenses have an average frequency inany direction of 5 to 250 complex lenses/mm.
 9. The transparentpolymeric film of claim 8 wherein the complex lenses have an averagefrequency in any direction of 22 to 66 complex lenses/mm.
 10. Thetransparent polymeric film of claim 1 wherein the complex lenses have anaverage width in the x and y direction in the plane of the film of 3 to60 microns.
 11. The transparent polymeric film of claim 10 wherein thecomplex lenses have an average width in the x and y direction of 15 to40 microns.
 12. The transparent polymeric film of claim 1 wherein thecomplex lenses comprise minor lenses wherein the diameter of the smallerlenses is on average less than 80% of the diameter of the major lensthey are associated with.
 13. The transparent polymeric film of claim 12wherein the number of minor lenses per major lens is, on average, 2 to60.
 14. The transparent polymeric film of claim 12 wherein the number ofminor lenses per major lens is, on average, 5 to
 18. 15. The transparentpolymeric film of claim 1 wherein the complex lenses comprise a multipleof minor lenses wherein the minor lenses have, on average, a width inthe x and y direction of 2 to 20 microns.
 16. The transparent polymericfilm of claim 15 wherein the complex lenses comprise a multiple of minorlenses wherein the minor lenses have, on average, a width in the x and ydirection of 3 to 8 microns.
 17. The transparent polymeric film of claim1 wherein the complex lenses are composed of a material that comprisesan olefin repeating unit.
 18. The transparent polymeric film of claim 1wherein the complex lenses are composed of a material that comprises acarbonate repeating unit.
 19. The transparent polymeric film of claim 1wherein the complex lenses are composed of a material that comprises anester repeating unit.
 20. The transparent polymeric film of claim 1wherein the transparent film is composed of a material that comprises anester repeating unit.
 21. The transparent polymeric film of claim 1wherein the transparent film is composed of a material that comprises acarbonate repeating unit.
 22. The transparent polymeric film of claim 1wherein the transparent film are composed of a material that comprisesan olefin repeating unit.
 23. The transparent polymeric film of claim 1wherein the transparent film is composed of a material that comprisestri acetyl cellulose.
 24. The transparent polymeric film of claim 1wherein the diffuse light transmission is greater than 50%.
 25. Thetransparent polymeric film of claim 1 wherein the diffuse lighttransmission is 80 to 95%.
 26. The transparent polymeric film of claim 1wherein the diffuse light transmission is greater than 92%.
 27. Thetransparent polymeric film of claim 1 wherein the complex lenses aresemi-spherical.
 28. The transparent polymeric film of claim 1 whereinthe complex lenses are aspherical.
 29. The transparent polymeric film ofclaim 1 wherein the complex lenses have a height/diameter ratio of 0.03to 1.0.
 30. The transparent polymeric film of claim 29 wherein thecomplex lenses have a height/diameter ratio of 0.25 to 0.48.
 31. Thetransparent polymeric film of claim 1, having a thickness of less than250 micrometers.
 32. The transparent polymeric film of claim 1, having athickness of 12.5 to 50 micrometers.
 33. The transparent polymeric filmof claim 1 wherein the elastic modulus of the transparent polymeric filmis greater than 500 MPa.
 34. The transparent polymeric film of claim 1wherein the film is comprised of at least two integral layers, the firstlayer containing the complex lenses and the second serving as thesubstrate for the first layer.
 35. A back lighted device comprising alight source and a transparent polymeric film comprising a plurality ofcomplex lenses on a surface thereof and having a diffuse lighttransmission of at least 65%.
 36. A liquid crystal device comprisingalight source and a transparent polymeric film comprising a plurality ofcomplex lenses on a surface thereof and having a diffuse lighttransmission of at least 65% wherein the transparent polymeric film islocated between the light source and a polarizing film.
 37. A componentfor a liquid crystal display device comprising a light source and alight diffuser comprising a transparent polymeric film containing aplurality of complex lenses on a surface thereof and having a diffuselight transmission of at least 65%.
 38. A method for forming a pluralityof polymeric complex lenses in a desired pattern on a transparentsupport comprising the step of coating a melted layer of a polymericmaterial onto the support and cooling the material while subjecting thelayer to contact with a form having a pattern corresponding to thenegative of the desired lens pattern.
 39. A method for forming aplurality of polymeric complex lenses in a desired pattern on atransparent support comprising continuously casting the polymericmaterial onto the support on a chill roll and cooling the material whilesubjecting the layer to a contact with a form having a patterncorresponding to the negative of the desired pattern.
 40. A transparentpolymeric film having a top and bottom surface comprising a plurality ofcomplex asymmetric lenses on at least one surface thereof.